The electrophoretic process of separation of soluble or particulate ionized matter is potentially complicated by convective effects. These may be caused by unequal temperature distribution, due to Joule heating, or unequal solute concentration, due to resolution of the sample into sharply compartmentalized individual zones. Stabilization against these convective disturbances is essential. The most common way to avoid convection is to work in gels, or columns packed with finely dispersed matter, such as glass beads, agarose granules, starch granules, etc., whereby electrophoresis is carried out in the interstitial capillary bed formed by these materials. Another way to stabilize against convective flow is to create a density gradient using an inert solute, such as sucrose. A third way was developed by Hjerten*, who utilized horizontal tubes, slowly rotating around their axis. Thus, gross convection is avoided, because of the continuous change in the direction of the gravity vector. This is akin to the commonly used clinostats in biological experiments. FNT * S. Hjerten: "Free Zone Electrophoresis", Almqvist & Wiksells, Uppsala, 1967.
No matter what principle of stabilization is employed, separation is easily achieved by the application of a D.C. electrical field. The major problem is not to achieve separation, but the actual physical isolation of the separated fractions. A number of techniques have been used, as for example, simple sectioning of gels, elution of powder-filled columns, separation of samples by means of careful aspiration with a syringe, interposition of a sample-impermeable dialyzing membrane in the migration pathway coupled with a transverse flow of buffer over the surface of the membrane, draining of density stabilized columns, etc.
A preliminary search of the prior art revealed the following U.S. Pat. Nos. as representing what appeared to be the best prior art relating to the subject matter of the present invention: Anderson et al., 3,927,826, Waterman, 2,849,394, Magnusen et al., 2,992,979, Smyth et al. 3,844,926.
The U.S. Pat. No. to Smyth et al. 3,844,926 shows a separating apparatus suitable for electrophoretic separation and including an uninterrupted annular chamber defined by coaxial outer and inner walls, wherein the outer wall rotates. The electric field is radially oriented across the lumen.
Magnusen et al. 2,992,979 show a combination of centrifugal field and an electrical field to enhance electrophoretic separation. The electrophoresis is practiced on a sheet of absorbent material to stabilize the fluid system.
The Anderson et al. U.S. Pat. No. 3,927,826 shows the formation of electrophoresis gels using a rotor. Waterman 2,849,394 uses a rotating system including a rotating electrode for coalescing.
Thus, the need exists for a simple means of withdrawing fractions from an axially oriented electrophoresis tube particularly in the field of cell electrophoresis, such as for the separation of living cells, e.g. blood cells.